2019, 39(5): 573-581.
doi: 10.11728/cjss2019.05.573
Abstract:
Based on the Solar Wind Dynamic Pressure Pulse (DPP) events observed by the WIND spacecraft from 1995 to 2014, the distribution of the orientation and the type of DPPs is statistically analyzed. Firstly, the distribution of the angle △θ between the magnetic field vector in the preceding region and that in the succeeding region is well fitted by a piecewise function with double power-law distribution. Secondly, the Minimum Variance Analysis (MVA) method is used to determine the normal of DPP. In order to obtain a reliable normal of DPP, the MVA eigenvalue ratio λ2/λ3 ≥ 2 and △θ ≥ 30° are taken into constraints. The directions of the investigated DPPs mainly concentrate in a certain region of -50° ≤ θn ≤ 50°, 160° ≤ φn ≤ 250°, and the center of the investigated DPP is at the point of θ=-22.83°, φ=186.59°. Thirdly, DPP can be classified into four types of discontinuities such as Tangential Discontinuity (TD), Rotational Discontinuity (RD), Either Discontinuity (ED), and Neither Discontinuity (ND). The proportion of these four types of DPP is 46.37%, 19.57%, 27.49% and 6.57%, respectively. The results show that most DPP belong to TD, and the proportion of TD and RD are much larger than ED and ND during the solar minimum. The results would help to improve the accuracy of forecasting of the transit time between the WIND observation and the magnetosphere response and to study the formation mechanism of DPP.
